(a) Field of the Invention
The present invention relates to an electroless deposition of nano metallic silver. Specifically, the present invention relates to a method for an electroless deposition of silver on a non-conductive surface to have a good density, and a plate having the deposited metallic silver by the method. More particularly, the present invention provides a reflector used for a solar reflector or an optic reflector that the high reflectance is necessary.
(b) Description of the Related Art
Conventionally, methods for applying metallic luster to vehicles and components for electric home appliances can be classified into two methods, that is, a wet method and a dry method. First, a chromium plating method is generally used as the wet method, and a vacuum deposition method is generally used as the dry method. However, in the chromium plating method, a toxic wastewater is generated by hexavalent chromium. In the vacuum deposition method, a producibility is low due to a high price of investment in plant and equipment and a limitation of an processing amount according to a size of the equipment.
Meanwhile, a reflector such as a mirror generally has a thin reflective metal layer coated on a surface of a glass substrate. The metal layer directly coated on the glass substrate is conventionally a silver layer. However, another metal layer such as a copper layer may be employed. When the silver layer is used as a main reflective layer, in order to suppress a corrosion of the silver layer, a copper layer is formed as a protection layer for protecting the silver layer. In addition, so as to improve an anti-corrosion property and an abrasion resistance property, a paint layer may be formed on the silver layer or the copper layer.
Here, U.S. Pat. No. 4,737,188 discloses a conventional method for forming the silver layer used as the reflection layer. That is, a mixing solution that ammoniacal silver nitrate and a reducing agent containing a strong alkali are mixed is sprayed to a sensitized glass surface, and thus the silver layer is deposited on the glass.
However, if the silver layer is formed by the above conventional plating method, there are drawbacks that a reflectance is not high (about 80%) due to a low density of the silver layer and the light is leaked out. In addition, there is a serious problem that the reflectance is drastically reduced when the reflection substrate is exposed in the outer condition.
Particularly, in a large-scale reflector used for solar thermal power generation, if the reflectance is increased by only 1%, an operation period of a solar thermal power generation can be increased to twenty years. Also, an operation rate by reflectance (that is, an energy conversion rate) can be increased, thereby achieving an effect of energy generation. Thus, the reflector having a increased reflectance by only 1% is constantly necessary.
Meanwhile, Korean Patent No. 10-0766715 (Electroless Silver Plating Using Amine) relates to an electroless silver plating method generating a silver thin film on a substrate by using an electroless plating solution including silver ion and a reducing agent. Through controlling a relative concentration between the silver ion and amine, a size of silver particles forming the silver thin film can be freely controlled from several tens nanometers to several tens micrometers, and a thickness of the silver thin film formed on the substrate can be controlled. The obtained specimen has a density (surface roughness) less than 25 μm. In the density, the silver thin film may have properties in optics and luster to some degree; however, does not have a high reflectance. Furthermore, the contents related to a reflectance is not mentioned in the Korean Patent.
Japanese Laid-Open Patent Publication No. 2001-46958 (Formation of Coating Film Having Metallic Luster) relates to a method for forming a coating film having a metallic luster on a surface of a plastic molding for automobiles or domestic appliances. This discloses a plating method using a spray process having two nozzles simultaneously spraying silver nitrate and a reducing agent. This relates to a wet coating method for providing a metallic lusted on the plastic molding, and does not relate to a reflector having a high reflectance.